Several recent instances of tail-boom buckling have occurred after an autorotational touchdown in the OH-58A helicopter. These occurrences prompted the US Army Aviation System Command (AVSCOM) light observation helicopter (LOH) Project Manager to enter into a product improvement program (PIP) with Bell Helicopter Company (BHC) to define the problem and recommend a solution. This PIP task included computer studies, a shake test, and flight testing of a structurally instrumented OH-58A helicopter. The results of the PIP task, to date, indicate that the tail-boom buckling resulted from a resonant condition between the main rotor and the natural frequencies of the fore and aft pylon mode and the tail boom. This resonant frequency, 5 hertz, was likely to occur at high blade angles (100-percent collective) and low rotor speed (150 rpm) and was associated with large main rotor flapping excursions. Three solutions were considered: (1) change the natural frequencies of the fore and aft pylon mode and/or tail boom, (2) damp the pylon movement, and (3) eliminate the excessive blade flapping. The BHC chose the third solution by electing to restrict the maximum collective control travel which would, in turn, eliminate excessive flapping at low rotor speeds. The BHC testing showed that there was no degradation of helicopter performance as the result of the installation of an 80-percent collective pitch restriction device.